Did you move the game directory after installing it? Where did you install it to? Please also try to run it as admin. I have all my VNs installed under C:\VNs\; maybe that could help? I moved it from there to C:\ and just had to launch it twice as administrator and then it ran fine every time I ran it as administrator.
Nope, haven't moved the directory. When it installed, it created a new folder titled "2002_Others_Im_Gonna_Serve_You_4_516MB" with another folder inside that contained the game and all of its files. I could run the game just fine, and I was towards the end of the Chizuru route when I stopped playing that first time. Then when I loaded it up the next day, if I pressed any of the options in the main menu, the game froze and I had to force quit. It couldn't get past the main menu at all.
I find it rather bizarre. I was able to load up the game and play without issue, even save/load to go back to different options and go through the extras menu. It was functioning perfectly and now it just doesn't. Went ahead and uninstalled, then reinstalled. Unfortunately the same issue persists where it dies if I interact with any of the menu options, although I do not get the registration error anymore.
I have all my VNs in a folder just for VNs and run everything as administrator, so I'm clueless as to why this is happening.
EDIT: I'm going to keep trying a few things and see if they make a difference. Let me know if you have any ideas.